The Andean orogenic period began in the Albian and consisted of at least 6 discrete compressional phases which are Albian to late Miocene in age. Deformation migrated progressively toward the Amazonian foredeep. The major Andean structures in central and northern Peru are related to the Eocene (Incaic), early Miocene (Quechua 1) and late Miocene (Quechua 3) phases. The Maranon thrust and fold belt (MTFB) which bounds the western Cordillera to the NE rose in the Eocene. It was reactivated partly by the Quechua 1 phase, which also folded the Altiplano farther E and possibly part of the eastern Cordillera. The sub-Andean thrust and fold belt (STFB) is related to the Quechua 3 phase. In both MTFB and STFB the imbricate thrusts merge at depth in large décollement faults. Gravity sliding does not play a dominant role, for these faults have to be rooted westward in the pre-Andean basement. The corresponding crustal shortening played a significant part in the creation of the sialic root of the Andes.

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